In the area of water treatment, such as ground water or industrial waste water treatment, there is an ever-increasing need to remove undesirable and even toxic contaminants, particularly heavy metal contaminants, from water. Many industrial processes utilize aqueous solutions of heavy metals, such as lead, in manufacture of batteries, and chromium or copper in electroplating solutions.
Unfortunately, the removal of such heavy metals from the aqueous solutions used in these processes has proven to be not only difficult but expensive. Prior art processes have utilized quite expensive adsorbents, such as activated carbon, activated sludge, various types of natural clays, carbon aerogels, coirpith carbon, natural zeolites and even date pits. Likewise, heavy metal removal can be accomplished through expensive ion exchange resins.
U.S. Published Patent Application No. 2009/0184054 to Crawford et al., incorporated by reference herein, discloses an adsorptive bed having hydrous iron oxide and calcium carbonate materials. The adsorptive bed is useful in water treatment applications for removing metal contaminants, particularly for removing arsenic-containing ions.
U.S. Pat. No. 4,059,513 to Zadera, incorporated by reference herein, discloses treating high sulfate content water in a multistage process to remove sulfate and hardness. Sulfate concentration is reduced in the first stage of the process by addition of calcium hydroxide. Calcium concentration is reduced in the second stage of the process by reaction of carbon dioxide or bicarbonate and calcium and hydroxide ions from the first stage of the process, forming insoluble calcium carbonate.
U.S. Pat. No. 5,601,704 to Salem et al., incorporated by reference herein, discloses an automatic feedback control system for a water treatment apparatus, such as a recirculating solids contact clarifier, that maintains steady-state operation of the clarifier by accurately measuring the concentration of suspended solids at designated portions of the clarifier and automatically adjusting clarifier variables to maintain optimum conditions despite changes in the inlet flow rate, composition or temperature.
U.S. Pat. No. 5,266,210 to McLaughlin, incorporated by reference herein, discloses treating wastewater contaminated with heavy metals in a multi-stage process. In a first stage, wastewater is treated with an effective amount of calcium oxide and/or calcium hydroxide in the form of lime to adjust the pH so that various metals in the water become insoluble. Gypsum formation may also occur if sulfate ions are present in the wastewater. In a second stage, an effective amount of sodium carbonate is added in the form of soda ash to allow formation of calcium carbonate. In a third stage, a coagulant, preferably a polymer, is added to facilitate the formation of a sludge comprising heavy metals, gypsum and calcium carbonate. In a final stage, the pH of the resulting effluent may be adjusted with a suitable acid, such as hydrochloric acid, to attain acceptable discharge requirements. The sludge formed is substantially stable and dewatered and has low toxic metal leaching characteristics.
U.S. Pat. No. 4,338,200 to Zeijlstra, incorporated by reference herein, discloses a process for the removal of heavy metal ions, particularly chromium, lead and/or zinc ions, from aqueous liquids by precipitation wherein the aqueous liquid containing the heavy metal ions and an aqueous liquid containing a base which precipitates the heavy metal ions in the form of their hydroxide or basic salt are added simultaneously to an amount of water at a pH between 5 and 10 and a temperature between 60° and 100° C. and the pH and the temperature are maintained in the specified ranges during the precipitation.
U.S. Pat. No. 5,370,827 to Grant et al., incorporated by reference herein, discloses treating solutions such as for example drinking water, ground water and extracting solutions contaminated with heavy metals and radioactive species, singly or in combination, by first treating the contaminated solution with silicate and ammonium hydroxide solution precipitants. Then the contaminated solution is separately treated with an acid which gels, polymerizes and/or precipitates the contaminant-containing silica matrix to form an easily dewaterable and separable solid. The solid contaminants are readily removed from the cleansed solution by filtration means. The process utilizes a novel combination of steps which maximizes contaminant removal, minimizes waste volume, and produces a treatable waste solid. The preferred precipitants are sodium silicate, and ammonium hydroxide. The preferred mineral acid is hydrochloric acid.
However, none of the above-discussed references discloses or suggests a relatively inexpensive but highly effective adsorbent composition for removal of heavy metal contaminants from contaminated water streams. Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.